Deepwater blowout preventer systems are major pieces of capital equipment landed on the ocean floor in order to provide pressure protection while drilling holes deep into the earth for the production of oil and gas. The typical blowout preventer stacks have an 18-xc2xexe2x80x3 bore and are usually of 10,000 psi working pressure. The blowout preventer stack assembly weighs in the range of five to eight hundred thousand pounds. It is typically divided into a lower blowout preventer stack and a lower marine riser package.
The lower blowout preventer stack includes a connector for connecting to the wellhead at the bottom and several individual ram type blowout preventer assemblies, which will close on various pipe sizes and in some cases, will close on an open hole with what is called blind rams. Characteristically there is an annular preventer at the top, which will close on any pipe size or close on the open hole.
The lower marine riser package typically includes a connector at the bottom for connecting to the lower blowout preventer stack, a single angular preventer for closing off on any piece of pipe or the open hole, a flex joint, and a connection to a riser pipe which extends to the surface to the drilling vessel.
The purpose of the separation between the lower blowout preventer stack and the lower marine riser package is that the annular blowout preventer on the lower marine riser package is the preferred assembly to be used. When it is used and either has a failure or is worn out, it can be released and retrieved to the surface for servicing while the lower blowout preventer stack maintains pressure competency on the wellhead. The riser pipe going to the surface is typically a 21xe2x80x3 O.D. pipe with a bore larger than the bore of the blowout preventer stack. It is a low pressure pipe and will control the mud flow which is coming from the well up to the rig floor, but will not contain the 10,000-15,000 psi that the blowout preventer stack will contain. Whenever the high pressures must be communicated back to the surface for well control procedures, smaller pipes on each side of the drilling riser, called the choke line and the kill lines provide this function. These will typically have the same working pressure as the blowout preventer stack and rather than have an 18-xc2xe-20xe2x80x3 bore, they will have a 3-4xe2x80x3 bore.
These pipes come down on each side of the drilling riser, go past flex joints, to an area on each side of the connector connecting the lowering riser package to the lower blowout preventer stack. At this point they are connected to pipes which go down the lower blowout preventer stack and enter the bore of the lower blowout preventer stack, near the bottom of the blowout preventer stack. One of these lines is called the choke line, and has a general job description of allowing high pressure well fluids to flow up across chokes during the well control operations. The line on the opposite side is typically called the kill line and it is attached below the lowest blowout preventer ram and has a general job description of communicating a heavy fluid to be pumped down into the well to kill the well. Killing the well means that the pressure in the formation is high enough to overcome the pressure head of the fluid in the bore. Killing the well is placing heavy enough fluid in the well bore to overcome the formation pressures. When the lower marine riser package is disconnected from the lower blowout preventer stack, the choke and kill lines must be disconnected. There are typically two types of connectors for this application, a passive connector and an active connector. The passive connector is typically a straight stab and would typically have a seal O.D. of about 4-xc2xdxe2x80x3. As the stab is on about a 5 ft. radius from the centerline of the blowout preventer stack, if one of these units is pressured to 10,000 psi it exerts a force of approximately 160,000 lbs. on the blowout preventer stack or puts a moment of approximately 800,000 ft. lbs moment on the blowout preventer stack connector. This is a substantial force to be withstood and requires a redesign and reinforcement of the blowout preventer stack to accommodate these high forces.
The connector type choke and kill connector literally engages a small connector similar to the one that is on the centerline of the blowout preventer stack. By having an actual connector on the choke or kill connector the pressure force is taken within the connector and eliminates the destructive moment forces on the blowout preventer stack frame. A problem can occur in this design in that when the connector must be released in an emergency situation such as when the vessel has lost control and is being driven off location on the surface, the connector may not release. If the connector does not release in a drive off situation, the unit will be torn in half causing substantial damage to the blowout preventer stack, making it expensive and difficult to recover. Literally if a connector does not release and the blowout preventer stack is released, the recovery and repair is a multi-million dollar repair operation. An additional problem with conventional choke and kill connectors is that the choke and the kill lines are a pipe as long as 12,000 feet back to the surface, full of expensive drilling mud. When the open marine riser is released and the connector is released, the entire column of mud is spilled onto the ocean floor, representing not only a high cost but pollution potential. The conventional solution to this is the addition of a high pressure failsafe gate valve on the choke line and the kill line, along with additional required control functions for the valve.
The object of this invention is to provide a connector which is a passive connector which does not lock onto the lower mandrel, but also does not provide a separation force to be sustained by the blowout preventer guide frame and lower marine riser hydraulic connector.
A second object of the present invention is to provide a means for integral valving to retain the drilling mud in the choke and kill lines.
A third object of the present invention is to provide redundant re-energizeable sealing.
Another object of the present invention is to provide a connector which is tolerant of real-world manufacturing and installation conditions.